1. Field of the Invention
The present invention relates to multi-layered anti-reflection coating to be applied to a substrate, and more particularly to an anti-reflection coating for use with a plastic substrate to reduce reflectance of light.
2. Description of the Prior Art
A double-layered anti-reflection coating for use with a plastic substrate has been proposed in Japanese Laid-Open Patent Publication No. 56-110901. The coating comprises a first layer furthest from the substrate made of MgF2 and having an optical thickness of .lambda./4, and a second layer made of A1203 and having an optical thickness of .lambda./16, wherein .lambda. represents a design wavelength.
Although the above coating provides sufficient reflectance reducing effect, however, its durability is not sufficient for practical use. Therefore, if the coating is applied to an outer surface exposed to the outside of the device, for example, to an outer surface of an eyepiece lens element of a finder optical system, its optical performance may be deteriorated as time goes on.